Detailed restorations
were constructed from two sections across a single salt-detached thrust
structure in the deep-water Lower Congo Basin. Although the two sections
are only 4 km apart along strike, their structural style and deformation
timing are very different. The northern section intersects a thrust fault
overriding a low salt anticline, whereas the southern section intersects
a large, pinched-off salt diapir. The northern section displays little
or no Tertiary deformation, but the southern section shows all Tertiary
units thinning over the arched crest of the diapir, and a large normal
fault offsetting the seafloor. Restoration of the northern section suggests
that the preexisting salt anticline controlled the location and trend
of the subsequent thrust fault. Formation of the thrust fault can be dated
by change from symmetric to asymmetric depositional patterns. Bed rotation
and stratigraphic thinning in the hanging wall were caused by translation
up the thrust ramp. Late salt expulsion from the buried anticline folded
the thrust. Restoration of the southern section shows that the preexisting
diapir localized the thrust fault. Bed rotation and stratigraphic thinning
during diapir shortening were caused by salt flow, not translation up
a thrust ramp. Diapir pinch-off was recorded by the end of salt extrusion.
The Tertiary deformation that was absent to the north was probably not
due to shortening of the structure. Instead, we interpret a period of
late salt inflation, probably fed by salt escaping from severe shortening
to the south of the study area. Not all thick arched roofs are contractional!